Doubtful respect for such an apparition (7)
I believe the answer is:
spectre
'an apparition' is the definition.
(spectre is a kind of apparition)
'doubtful respect' is the wordplay.
'doubtful' indicates an anagram.
'respect' is an anagram of 'SPECTRE'.
'for such' is the link.
(Other definitions for spectre that I've seen before include "Sceptre (anag.)" , "after-image?" , "'Phantom, shade (7)'" , "Wraith" , "spirit" .)